A disk drive unit particularly mounted in an automobile should be designed so that no replay defect or interruption would occur even when it is subject to vibrations and shocks occurring during driving of the automobile. To this end, a variety of countermeasures have been developed and proposed so far in the art. For example, one conventional disk drive unit for automobiles overcomes this problem by a signal processing approach. In this approach, information having been read out from the disk is compressed and then stored in a memory. The stored information is then decompressed for replay. When information recorded in one record block fails to be read due to shocks or vibrations, another try for reading the information is made again to the same record block during which information already stored in the memory would be replayed to prevent the replay interruption.
Another approach to overcome the problem is a mechanical solution that employs an elastic support for supporting a mechanism such as an information pick-up device for picking up information. Examples of the elastic support are an oil damper, elastic damper, and spring. Generally, each of the mechanical dampers is improved so that it has a certain natural frequency capable of effectively reducing vibrations and shocks which would otherwise provide an adverse effect to an internal mechanism of the unit.
For example, JP (A) 3-234940 discloses an oil damper having a cylindrical member or housing made of rubber in which silicone oil with high viscosity is encapsulated. The oil damper is formed at its center with a bearing recess for supporting a shaft of a disk bearing mechanism and a plurality of resisting portions extending outwardly from the bearing recess. With this oil damper, vibrations and shocks are reduced significantly by elastic deformations of the resisting portions as well as by the viscous silicone oil. The cylindrical member, however, since it encapsulates the silicone oil and carries the bearing recess and resisting portions, is considerably complicated in structure. Also, the cylindrical member needs another member such as a support flange made of material different from the cylindrical member for holding the oil damper in a stable position. Further, since the major part of the damper is made of elastic material which is easily deformed by an external force, another supporting member such as a spring is required for positively supporting the disk drive unit. Furthermore, the oil damper allows the shaft to move in a wide range, which requires an extended space to prevent mechanical collisions in the disk drive unit. Moreover, it is difficult to make one natural frequency in one direction so different from that in another direction.
JP (A) 1-92984 discloses another disk drive unit in which a frame carries an optical card which moves in one direction on the frame. An optical head is supported on the card so that it moves in another direction perpendicular to the one direction. The frame is supported through vibration-proof members on a housing of the device. The vibration-proof member, made of elastic material such as rubber and formed with a horizontal through-hole, is characterized in that a flexibility in the first direction along which the optical head moves is greater than that in the second direction perpendicular to a major surface of the optical card, and the flexibility in the second direction is greater than that in the third direction along which the optical card moves.
With this disk drive unit, when trying to provide respective natural frequencies for the first to third directions, respectively, the natural frequency of the optical head becomes closer to those of the vibration-proof member. This would cause a resonance between the vibration-proof member and the optical head to eventually increase the reading defects. Also, since the vibration-proof member is secured by the use of screws, it should be formed with two portions, rigid portions suitable for screw mounting and flexible portions suitable for reducing the transmitted vibrations and shocks, which makes the replay device costly. Further, the card-like information bearing member is moved linearly, which requires a larger space than the replay device using disks.
JP(A) 2-61881 discloses another disk drive unit in which an optical pick-up device is mounted so that it moves in a radial direction of a disk. The pick-up device is supported on a disk drive mechanism mounted through a vibration-proof member on a cabinet. The vibration-proof member, which is made of elastic material such as rubber and in the form of a cylinder having an elliptical cross section, is arranged so that its longitudinal axis is oriented perpendicular to a major surface of the disk. In addition, the vibration-proof member is designed so that its elasticity in a direction along which the pick-up device moves (i.e., first direction) is less than those in second and third directions perpendicular to each other and to the first direction. However, the vibration-proof member can resonate with the optical head. Also, the vibration-proof member is fixed to the cabinet and disk drive mechanism with its outer grooves in engagement with holes provided in the cabinet and disk drive mechanism. This makes assembly of the vibration-proof members complicated. In addition, the vibration-proof members can be moved out of corresponding holes when subject to a drop shock, which may damage mechanisms in the disk drive unit. To prevent this, another damper should be provided, which increases the size of the disk drive unit and the number of parts, making the disk drive unit costly.
As described above, expected is a small, inexpensive, and simple damper with suitable damping features and which is not deformed excessively, and which does not require a fixing member or additional spring member.
Also expected is a damper which can be easily designed so that its natural frequencies in different directions can be increased or decreased relative to those of the optical head.